Power combining networks are used to combine the power generated by a group of amplifiers into a single output. Power combining networks provide solutions for many applications that require more output power than can be provided using a single conventional amplifier. For example, power combining networks are commonly used to broadcast signals in satellite communication systems such as Satellite Digital Audio Radio Service (SDARS) systems and Direct Broadcast Satellite (DBS) systems.
FIG. 1 is a schematic diagram depicting the primary components of a conventional eight-input power combining network 10. As shown in FIG. 1, power combining network 10 includes eight amplifiers 11, which are each fed a common signal in parallel. Each of amplifiers 11 is isolated from the rest of network 10 by an isolator 12. Isolator 12 intercepts power reflected back towards amplifier 11 from network 10 and redirects that power into load 13. The output of each amplifier 11 is coupled to a first stage of power combiners 14 via a redundancy switch 15. Using three stages of power combiners 14, the output power from each of the eight amplifiers 11 is combined into a single output signal.
A significant advantage of a power combining network is the ability of the network to compensate for amplifier failure. Typical power combining network designs, especially those used in satellite communication systems, include redundant amplifiers. For example, an eight-amplifier system such as that shown in FIG. 1 will usually have ten to twelve amplifiers. To simplify the drawing, redundant amplifiers are not depicted in FIG. 1. If one of amplifiers 11 fails, redundancy switches 15 are used to disconnect the output of the failed amplifier 11 from the first stage of power combiners 14 and connect one of the redundant amplifiers in its place. In this manner, power combining network 10 maintains a desired output power in the event of amplifier failure.
A problem arises when the number of amplifier failures exceeds the number of redundant amplifiers in the system. In an ideal system, the power loss (in dB) of an N-input system in this situation is                     10        ·                              log            10                    ⁡                      (                                          N                -                m                            N                        )                                              (        1        )            where N is the number of amplifier inputs in the system and m is the number of failed amplifiers (with m<=N−1). However, the power loss suffered by a conventional system is significantly greater than that of an ideal system. This difference is better understood by examining the operating characteristics of network 10 depicted in FIG. 1.
Power combiner 14 is typically implemented using a four-port waveguide power combiner to handle the power necessary for most satellite applications. Signals fed into the two input ports of power combiner 14 constructively combine into a single signal. If the two signals are appropriately phased with respect to each other, a single signal with twice the power is output from one of the output ports. If the two signals are not phased correctly with respect to each other, a portion of the output power is diverted to load 16 attached to the other output port. When an amplifier fails, and therefore does not provide a signal to one of the input ports, an ideal system would pass the power of the signal of the operational amplifier connected to the power combiner through to the next stage of power combiners. However, in a conventional system a significant portion of that power is diverted into load 16. Accordingly, the power loss (in dB) from one or more failed amplifiers in a conventional N-input system is                     10        ·                                            log              10                        ⁡                          (                              (                                                      N                    -                    m                                    N                                )                            )                                2                                    (        2        )            where N is the number of amplifier inputs in the system and m is the number of failed amplifiers (with m<=N−1).
FIG. 2 is a graph showing the power loss (in dB) due to failed amplifiers in a sixteen-input power combining network. The dotted line in the graph shows the power loss suffered by an ideal system as the number of failed amplifiers increases. The dashed line shows the power loss suffered by a conventional system as the number of failed amplifiers increases. As shown in the graph, the power loss suffered by a conventional system is greater than that suffered by an ideal system and the difference increases with the number of failed amplifiers.
Accordingly, a need exists for a new power combining network design. The new power combining network should improve network efficiency and recover more power in the event of amplifier failure. Furthermore, the new power combining network should be cost effective and minimize any additional hardware required.